The Applicants' French patent application FR 94 08 337 discloses the general principle of tracking a force by an inverse model using an open loop scheme.
In accordance with the essential characteristics of the semi-active damper controlled by a control circuit as described in that French patent application FR 94 08 337, the control circuit includes a direct control loop including an inverse model of the damper.
In addition, the inverse model of the damper determines a value for an ideal electric current i.sub.th for controlling a compression controlled-restriction valve and an expansion controlled-restriction valve on the basis of a measured value for a relative speed y between two ends of the damper, and on the basis of a force reference value Fc.
A force feedback loop adds to the ideal control electric current i.sub.th a proportional type corrective term .delta.i so as to take into account a force error .epsilon.F between the reference force value Fc and the measured value of the force F actually exerted.
The inverse model of the damper is defined by the expressions: ##EQU1## where K.sub.13 and K.sub.23 are positive constants that depend on the size of the actuator, on the physical characteristics of the oil, and also on the flow rate gain of the hydraulic valves.
The inverse model of the damper as defined in this way assumes that the fluid is incompressible.
Nevertheless, this assumption is not valid in all applications.